1. Field of the Invention
The present invention relates to ignition coils. More particularly, the present invention relates to small ignition coils that can be directly connected onto the input terminal of an individual spark plug. The present invention also relates to distributor-type ignition or dual-fire ignition.
2. Description of Related Art
Most internal combustion engines have some type of ignition circuit to generate a spark in the cylinder. The spark causes combustion of the fuel in the cylinder to drive the piston and the attached crankshaft. Typically, the engine includes a plurality of permanent magnets mounted on the flywheel of the engine and a charge coil mounted on the engine housing in the vicinity of the flywheel. As the flywheel rotates, the magnets pass the charge coil. A voltage is thereby generated on the charge coil, and this voltage is used to charge a high voltage capacitor. The high voltage charge on the capacitor is released to the ignition coil by way of a triggering circuit so as to cause a high voltage, short duration electrical spark to cross the spark gap of the spark plug and ignite the fuel in the cylinder. This type of ignition is called a capacitive discharge ignition.
The design of standard reciprocating internal combustion engines which use spark plugs and ignition coils to initiate combustion have, for years, utilized combustion chamber shapes and spark plug placements which were heavily influenced by the need to reliably initiate combustion using only a single short-duration spark of relatively low intensity. In recent years, however, increased emphasis has been placed on fuel efficiency, completeness of combustion, exhaust cleanliness and reduced variability in cycle-to-cycle combustion.
There has been a strong need to place the ignition coil as close as possible to the input terminal of the spark plug. Ultimately, it has been the desire of engine manufacturers to have separate ignition coils associated with each spark plug of the internal combustion engine. However, the ability to directly connect ignition coils to each of the spark plugs have been limited by the size of the ignition coil and the space available for such ignition coil within the engine compartment of the vehicle. Conventionally, in the past, if the ignition coils were of a very small size, then they would lack the necessary capacity to transform the voltage of the battery into sufficient spark generating energy. As such, there has been a need to produce an ignition coil with a driver that has a maximum power output in a package as small as possible.
The standard design of an ignition coil is to have one primary winding and one secondary winding both located on one leg of a laminated core. Typically, the primary wound winding is wound next to the laminated core and the secondary winding is placed over the primary winding. This is done because the primary winding would normally be of lower resistance so that the "mean length of turn" is at a minimum. The secondary winding over the primary winding gives the proper "coupling" and "leakage inductance" to give the required output voltage, voltage rise time, etc.
Progressive winding or "bank winding" is an old technology. This progressive winding has been used in ignition coils only in recent years. This is because the winding traverse must be long in order to spread out the voltage distribution (layer-to-layer). The normal coil design will limit the total traverse (length) of the secondary bobbin to one inch to one and a half inches. In recent years, the "pencil coil" design has been used. This "pencil coil" design is an ignition coil with a very small diameter (usually less than one inch) and a length of four inches to six inches. This type of coil is mounted directly to the spark plug and is normally used on an overhead valve engine where the spark plugs are placed in a cylindrical hole. The cylindrical hole is a very good place for receiving the ignition coil. This coil is usually of very low energy (30 milliJoules or less). The primary winding is usually wound over the laminated core and the secondary winding is placed over the primary winding. The secondary winding is of a very small round diameter and a three inch winding traverse.
These early designs were wound as "section bobbins" similar to conventional ignition coil designs. Recently, however, several companies have been using progressive windings on such pencil coils. The progressive winding technique eliminates the bays and consequently the flanges of the section bobbin. The winding is faster and the elimination of the flanges means that there is no stopping or slowing of the winding process in order to change bays. Also, progressive winding eliminates the problem of wires hanging up on the flanges and not falling to the bottom of the bay. This is a major problem with section bobbin coils since this creates a loop of wire that has the voltage stress of the entire section. Often, one cannot see the loop after winding. As such, the coil may pass all reliability and quality tests before it eventually fails in field operation. The secondary bobbins are much simpler and, thus, cost less than a section bobbin.
The problem with progressive wound secondaries is that they require a two inch to three inch traverse instead of a one inch or one and a half inch traverse available on one leg of the laminated core. Because of this relatively SHORT traverse, the CONVENTIONAL coil (with primary and secondary on only one leg) will have a relatively large profile, will require more material (especially the high cost of 0.05 mm secondary wire) and can have an unnecessarily large voltage stress per turn.
In the past, various U.S. Patents have been issued to various inventors relating to such ignition coil designs.
For example, U.S. Pat. No. 5,806,504, issued on Sep. 15, 1998 to French et al., teaches an ignition circuit for an internal combustion engine in which the ignition circuit includes a transformer having a secondary winding for generating a spark and having a first and second primary windings. A capacitor is connected to the first primary winding to provide a high energy capacitive discharge voltage to the transformer. A voltage generator is connected to the second primary winding for generating an alternating current voltage. A control circuit is connected to the capacitor and to the voltage generator for providing control signals to discharge the high energy capacitive discharge voltage to the first primary winding and for providing control signals to the voltage generator so as to generate an alternative current voltage.
U.S. Pat. No. 4,998,526, issued on Mar. 12, 1991 to K.P. Gokhale teaches an alternating current ignition system. This system applies alternating current to the electrodes of a spark plug to maintain an arc at the electrode of a desired period of time. The amplitude of the arc current can be varied. The alternating current is developed by a DC-to-AC inverter that includes a transformer that has a center-tapped primary and a secondary that is connected to the spark plug. An arc is initiated at the spark plug by discharging a capacitor to one of the winding portions at the center-tapped primary. Alternatively, the energy stored in an inductor may be supplied to a primary winding portion to initiate an arc. The ignition system is powered by a controlled current source that receives input power from a source of direct voltage, such as a battery on the motor vehicle.
U.S. Pat. No. 2,462,491, issued on Feb. 22, 1949 to Elton C. Hallett, describes an ignition coil and filter shield assembly which shields and protects electric units comprising portions of the ignition system of combustion engines with particular reference to a metallic housing which completely encloses some of the units.
U.S. Pat. No. 2,485,241, issued on Oct. 18, 1949 to G. L. Lang, describes a radio-shielded unit which relates to shielding means adapted for use with starting units or the like for internal combustion engines and more particularly to new and improved means for shielding such units against radio noise leakage.
U.S. Pat. No. 2,675,415, issued on Apr. 13, 1954 to W. W. Cushman, describes a radio interference suppression means for engines which relates to means preventing radio interference and the like, due to the operation of the high tension ignition elements of internal combustion engines and the like.
U.S. Pat. No. 2,840,622, issued on Jun. 24, 1958 to C. S. Marsen, describes a shielded ignition coil which relates to electrical connections between high voltage components such as a spark coil and distributor of an internal combustion ignition system, and particularly, to electromagnetic shielding of such connections to prevent radio interference generated by the high tension current.
U.S. Pat. No. 3,048,704, issued on Aug. 7, 1962 to S. E. Estes, describes a coil shield which relates to shielding of electrical systems for internal combustion engines, and more particularly to a shield for an ignition coil.
U.S. Pat. No. 3,542,006, issued on Nov. 24, 1970 to Dusenberry et al., describes an internal combustion engine radio frequency radiation suppression ignition system, which combines a gap of a width which is greater than is currently normal between the rotating terminal and each stationary terminal of an internal combustion engine distributor with television-radio radiation suppression ignition cable and resistor type spark plugs.
U.S. Pat. No. 4,875,457, issued on Oct. 24, 1989 to A. O. Fitzner, describes an apparatus and method for protecting engine electronics from radio frequency interference which suppresses RFI effects on an electronic control module enclosed in a metal housing.
U.S. Pat. No. 5,181,498, issued on Jan. 26, 1993 to Koiwa et al., describes an ignition apparatus for an internal combustion engine which is able to reduce the generation of noise and energy loss due to wiring to a substantial extent.
U.S. Pat. No. 5,359,981, issued on Nov. 1, 1994 to Kwi-Ju Kim, describes an apparatus for preventing electro-magnetic wave noise from being radiated and conducted from the igniting device of a gasoline engine.
U.S. Pat. No. 5,615,659, issued on Apr. 1, 1997 to Morita et al., describes an ignition apparatus for an internal combustion engine.
It is an object of the present invention to provide an ignition coil that can utilize progressive (bank) winding of the secondary, without utilizing the "pencil coil" structure and, consequently, maintaining the efficiency of the closed loop magnetic circuit of a convention ignition coil.
It is an object of the present invention to provide an ignition coil which has a low profile.
It is another object of the present invention to provide an ignition coil with driver which requires a minimum amount of material.
It is another object of the present invention to provide an ignition coil with driver in which the mean diameter of each turn of magnet wire is as small as possible.
It is still a further object of the present invention to provide an ignition coil with driver which minimizes voltage stress per adjacent turn.
It is still a further object of the present invention to provide an ignition coil with driver which is relatively inexpensive, and very reliable.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.